Re: [gentoo-user] Re: Change from udev to eudev?

[wabe]

Jonathan Callen <jcallen@g.o> wrote:

> On 06/09/2016 10:00 AM, Dale wrote:
> > waltdnes@××××××××.org wrote:
> >> On Thu, Jun 09, 2016 at 08:16:57AM -0500, Dale wrote
> >>> karl@××××××××.se wrote:
> >>>> Dale:
> >>>> ...
> >>>>> Can a system even boot without udev?
> >>>> Yes, use sys-fs/static-dev (unless you have some special boot
> >>>> requirements).
> >>> Well, I was talking about if udev was removed and then a reboot
> >>> was done.  I would think it would boot to a certain point then
> >>> when whatever started and needed devices to be created in /dev,
> >>> it would start failing.  I suspect this would vary depending on
> >>> the install as well.
> >>   You need *A* device-manager.  You can use udev, eudev,
> >> static-dev, mdev, whatever, but you need something.  Mind you,
> >> some software assumes or requires udev/eudev.
> >>
> >
> >
> > What I was referring to was if during this switch from udev to
> > eudev, someone rebooted without any dev manager at all.  In other
> > words, emerge -C udev and then reboot before emerging eudev or some
> > other dev manager.  I suspect that would get interesting pretty
> > quick.
> >
> > Dale
> >
> > :-)  :-)
> >
> >
>
> Actually, you no longer need a user-space device manager at all,
> unless you want to be able to access device nodes under /dev as a
> user that isn't UID=0 or has CAP_DAC_OVERRIDE.  The kernel provides a
> devtmpfs filesystem that will have every single device node that udev
> used to create (udev no longer even creates the devices -- it just
> relies on devtmpfs doing so), but most of them will be owned by 0:0
> (root:root) with permissions 0600; excepting certain nodes
> like /dev/null or /dev/zero, which will be owned by 0:0 with
> permissions 0666.  One other thing that udev does that you might rely
> on is to create symlinks like /dev/disk/by-label/*, which can be used
> by mount(8) if you specify LABEL=foo in /etc/fstab.  The only other
> things that I'm aware of udev doing is to rename network devices and
> (possibly) to notify other applications of changes, somehow (but I'm
> not sure that it actually does that).
>
> If you don't actually need any of that (you are working on an embedded
> system where you only need root anyway, for instance), then you can
> just use a bare devtmpfs without a device manager changing
> permissions, adding links, etc.

THX for all the information. Now I understand better what (e)udev is
doing.

--
Regards
wabe